<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="../412/lib/vue.js"></script>
</head>
<body>
    <div id="app">
        <h2>{{title}}</h2>
    </div>

    <script>
        const vm = new Vue({
            data:{
                title:"第五天"
            },
            methods:{},
            mounted(){
                document.getElementsByTagName('title')[0].innerHTML = this.title;
            }
        }).$mount("#app")
    </script>
</body>
</html>